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Nine in ten people around the world breathe air containing high levels of pollution, according to the latest data from the World Health Organization (WHO). The agency estimates that pollution causes 7 million deaths each year.

The latest WHO figures measure the amount of pollutants in the air in more than 4,300 cities, towns and other settlements in 108 countries around the world. More cities than ever are now monitoring their air quality.

“We are seeing an acceleration of political interest in this global public health challenge," said Dr Maria Neira, WHO’s Director of Public Health, Environmental and Social Determinants of Health.

“The increase in cities recording air pollution data reflects a commitment to air quality assessment and monitoring.

“Most of this increase has occurred in high-income countries, but we hope to see a similar scale-up of monitoring efforts worldwide.”

The data found that pollution levels are highest in south-east Asia, as well as the Middle East and north Africa – a geographical area categorised by the WHO as the eastern Mediterranean.

Pollution levels were also found to be high in low and middle-income cities in Africa and the western Pacific. Many of the world’s megacities have annual average pollution levels more than five times the WHO safe limit.

“There is no doubt that air pollution represents today, not only the biggest environmental risk for health, but this is a major challenge for public health at the moment – probably one of the biggest ones we are contemplating,” said Dr. Neira.

Ambient – or outdoor – pollution is responsible for 4.2 million deaths per year, while 3.8 million people die annually as a result of household air pollution caused by cooking and heating their homes with solid fuels.

Pollution contributes to death when fine particles of soot, dust and other materials found in polluted air enters the lungs and cardiovascular system.

In most cases air pollution is a contributory factor and not the primary cause of death.

Air pollution is increasingly recognised as a key risk factor for non-communicable diseases (NCDs), the biggest cause of death worldwide.

Twenty-five per cent of deaths due to heart disease and stroke, 43 per cent of deaths due to chronic obstructive pulmonary disease and 29 per cent of deaths due to lung cancer are linked to breathing poor quality air.

The WHO looked at the annual average concentration of two categories of fine particulate matter found in polluted air – PM10 and PM2.5.

PM2.5 pollutants – which include sulfate, nitrates and black carbon – are the most concerning for human health.

Countries are recommended to limit their average annual air pollution levels to 10 micrograms of PM2.5 for every cubic metre of air.

While the largely self-reported data shows that pollution remains high in much of the world, a number of countries – particularly in Europe and the Americas – have started to curb their pollution levels.

China, often regarded as one of the world’s worst polluters, has made surprising progress.

“China has declared a war on air pollution in a very strong political way,” said Dr Neira. “It might give us some hope that one of the world’s biggest countries that represents one of the major risks is taking these types of strong steps.”

A number of other countries such as India and Mexico have also taken positive steps on a smaller scale.

“If you have the minimum political will to do it and a little investment you will start to see see good results almost immediately,” said Dr Neira. “Scandinavia proves you can have a very strong economic development without destroying your environment and without at the same time destroying your health.”

The WHO believes that as countries increasingly recognise the link between high levels of air pollution and poor health outcomes, action to address climate change, although currently slow, is possible.

“The moment people start to recognise that this is affecting their own health and not just the planet or the future or what is happening many years from now – the moment they understand that this is linked to stroke, heart disease, chronic obstructive pulmonary disease, asthma, pneumonia and lung cancer – this will change completely,” said Dr Neira.